1. Field of the the Invention
The present invention relates to a drum-type weft yarn feeding device and, more specifically, to a technique for controlling the rotary motion of the rotary yarn guide of a drum-type weft yarn feeding device.
In the drum-type weft yarn feeding device of this kind, a length of a weft yarn necessary for one picking cycle or several picking cycles is measured and stored on a stationary measuring and storing drum by pulling out the weft yarn from a supply package and winding the same on the stationary measuring and storing drum, the free end of the weft yarn is restrained on the circumference of the drum with a restraining pin. The restraining pin is retracted to release the weft yarn for picking operation. Upon the release of the weft yarn, a picking nozzle jets a pressurized fluid into the shed of warp yarns to pick the weft yarn previously stored on the drum.
Ordinarily, the rotary yarn guide and the restraining pin are interlocked mechanically with the crankshaft of the loom in order to control the rotary yarn guide and the restraining pin in synchronism with the main weaving motion of the loom. However, on a high-speed loom, the rotary yarn guide and the restraining pin mechanically interlocked with the crankshaft are unable to follow the main weaving motion of the loom. Furthermore, the free selection of weft yarns for weaving operation multiple weft yarns is difficult. Such problems can be solved by driving the rotary yarn guide by an individual feed motor instead of the crankshaft through mechanical means. When such an individual feed motor is employed, the weft yarn feeding mechanism needs to control the feed motor.
2. Description of the Prior Art
Japanese Patent Laid-open Publication No. 59-204,947 discloses an invention in which the length of the weft yarn wound on a measuring and storing drum is detected optically to control the feed motor on the basis of the result of detection.
Incidentally, adverse effects affecting picking operation, such as resistance against pulling out the weft yarn from the measuing and storing drum, can be diminished by reducing the length of the weft yarn wound on the measuring and storing drum to improve picking conditions. However, the reduction of the length of the weft yarn stored on the measuring and storing drum required frequent on-off operation of the feed motor, which affects adversely to the feed motor resulting in unstable winding of the weft yarn on the measuring and storing drum.
On the other hand, the frequency of the on-off operation of the feed motor can be reduced by increasing the length of the weft yarn wound on the measuring and storing drum in one winding cycle. However, when a length of the weft yarn for a plurality of picking cycles is stored on the measuring and storing drum, a complicated separating mechanism for separating the loops of the weft yarns is necessary for preventing the entanglement of the weft yarn on the measuring and storing drum. Such a separating mechanism makes the constitution of the weft yarn feeding mechanism complicated and increases the load on the feed motor, and hence the weft yarn feeding mechanism requires a large feed motor.
Furthermore, the reliability of the optical sensor for detecting the length of the weft yarn wound on the measuring and storing drum is dependent on the type of the weft yarn. A mechanical sensor employing a detecting lever for detecting the length of the weft yarn wound on the measuring and storing drum increases the tension of the weft yarn being picked adversely affecting the stability of picking operation.
Japanese Patent laid-open Publication No. 58-31,145 discloses an invention in which a pulse motor is employed as the feed motor. The rotation of the pulse motor is regulated through an open-loop control mode by giving pulses corresponding to the necessary length of the weft yarn to the pulse motor. However, since the response speed of the pulse motor is not high enough for use on a high-speed loom such as a fluid jet loom. When pulses are given to the pulse motor at a rate exceeding the response speed of the pulse motor, the step-out of the pulse motor occurs and the pulse motor is liable to malfunction.